Nanoporous Silicon-Based Platforms for Biological Applications Fabricated by UV Laser Techniques

Nanostructured porous silicon (nanoPS) can be regarded as a complex network of silicon nanocrystals embedded in a porous matrix. NanoPS is fabricated by the electrochemical etch of silicon wafers in HF-based solutions. When crystalline Si is transformed into nanoPS, its intrinsic properties are altered owing to quantum confinement effects. That makes nanoPS an excellent candidate for the development of several applications in a broad range of fields including optoelectronics, photonics, and biomedicine.

Surface micro- and nano-patterning is becoming an important way to enhance the performance of materials. In particular, nanoPS patterns have been proposed for the fabrication of photonic devices, high-sensitivity sensors, etc. Different techniques have been used for the fabrication of patterns on nanoPS including microstructuring the crystalline silicon substrate before the electrochemical etching process, dry soft lithography, stamp pressing, etc. However, none of these methods has the capability to offer flex-ibility in the pattern design in a time-efficient process, in large areas, and in a single step pro-cess.

The present work reports on the fabrication of one- and two-dimensional platforms on nanoPS by phase-mask UV laser interference. This technique is a single-step and flexible approach to produce a large variety of patterns formed by alternate regions of almost untransformed nanoPS and regions where its surface has melted and transformed into Si nanoparticles.

By changing the main experimental parameters such as nanoPS layer porosity, average pore size, laser fluence or pattern period, the properties of the resulting structures can be controlled. These patterns have been proved to be good candidates for such applications as sensing and for the development of biological platforms.